A judge has found a Calgary man guilty of sexually assaulting three vulnerable women, one of whom he drugged, and another he suffocated and assaulted with a weapon at a rural home east of the city.

He was also convicted of uttering threats against a fourth woman.

Richard Mantha, 62, sat silently in a Calgary courtroom while the judge delivered her verdict Tuesday morning, almost exactly three years after his arrest.

He was convicted of six charges total.

He originally faced 20 charges involving seven women, mostly vulnerable sex-trade workers with addictions issues.

Justice Judith Shriar dismissed charges relating to two other complainants.

Charges involving a seventh complainant were previously dropped because the woman died during the lengthy court proceedings.

Police arrested Mantha following an investigation into women in Calgary’s sex trade being targeted, drugged and attacked.

The case was delayed several times as Mantha fired defence lawyers and suffered a stroke.

A sentencing hearing will take place at a later date.